Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $41.51   3.834%   $43.1015   $43.10   $43.10   $43.10  
  Purchase #2 $174.71   9.760%   $191.7617   $191.76   $191.75   $191.80  
  Purchase #3 $150.91   9.498%   $165.2434   $165.24   $165.25   $165.20  
  Purchase #4 $157.84   7.122%   $169.0814   $169.08   $169.10   $169.10  
  Purchase #5 $60.59   4.652%   $63.4086   $63.41   $63.40   $63.40  
  Purchase #6 $66.85   11.597%   $74.6026   $74.60   $74.60   $74.60  
  Purchase #7 $43.61   4.808%   $45.7068   $45.71   $45.70   $45.70  
  7 purchase totals = $696.02       $752.9060   $752.90   $752.90   $752.90